No abstract

The oriented in situ crystallisation of microporous manganese(II) formate [Mn(HCO 2 ) 2 ] on different porous supports (e.g. porous alumina and graphite) has been investigated. The anisotropic growth of Mn(HCO 2 ) 2 was examined by Xray diffraction (XRD) and scanning electron microscopy (SEM). The intracrystalline diffusion of methanol in Mn(HCO 2 ) 2 was studied by observation of the sorption kinetics by interference microscopy (IFM). It was found that untreated discs of porous alumina and graphite supports exhibit poor densities of Mn(HCO 2 ) 2 crystals per supported area. Even lower crystal densities are found for activated supports such as for alumina after basic treatment and for oxidized graphite supports. Improved results have been achieved by replacing formic acid by sodium formate in the synthesis

The mixed ionic-electronic conductor (MIEC) (Ba 0.5 Sr 0.5 )(Co 0.8 Fe 0.2 )O 3-δ (BSCF) is a renowned material with applications in membrane reactors and as cathodes in solid-oxide fuel cells. Despite BSCF's large oxygen permeabilities, long-time phase instability at intermediate temperatures has been reported. However, the mechanism of this decomposition is still unclear. Here, we present a study of the synthesis of BSCF and compare our results with those obtained from long-time decomposition. Rietveld and Le Bail analysis as well as transmission electron microscopy studies were applied to investigate the reaction sequence in BSCF formation. We are now able to draw the following conclusion about the reaction mechanism: the formation as well as decomposition is due to a reversible reordering of the hexagonal AO 3 -layer stacking sequence in the cubic perovskite, which can occur if the cubic BSCF is kept at temperatures below T ) 1173 K for long time periods, thereby leading to the decomposition of BSCF into a three-phase mixture. The driving force for this reaction was identified to occur at the cobalt site because cobalt prefers a low-spin configuration in the 3+ oxidation state. This reaction occurs only at temperatures below T ) 1173 K because of the oxidation of cobalt at low temperatures.

The intracrystalline concentration profiles during molecular uptake of methanol by an initially empty, single crystal of microporous manganese(II) formate (Mn(HCO2)2), representing an ionic inorganic-organic hybrid within the MOF family, are monitored by interference microscopy. Within these profiles, a crystal section could be detected where over the total of its extension ( approximately 2 microm x 50 microm x 30 microm) molecular uptake ideally followed the pattern of one-dimensional diffusion. Analysis of the evolution of intracrystalline concentration in this section directly yields the permeability of the crystal surface and the intracrystalline diffusivity as a function of the concentration of the total range of 0